Gripper for use with a lifting apparatus for gripping an article desired to be lifted

ABSTRACT

Disclosed is a gripper wherein between a pair of support plates extending from their upper ends connected to the lifting apparatus toward their lower ends there are provided a trapezoidal column presenting in cross section an isosceles trapezoid arranged with its bottom surface turned in said upper end and a pair of guide members having side surfaces arranged, respectively, in parallel with both inclination side surfaces of said trapezoidal column; and a pair of clamping members adapted to grip the article when allowed to slide toward said other end side are disposed, respectively, within a pair of elongate void spaces each defined between said inclination side surface of the trapezoidal column and said side surface of the guide member and united into one space on said lower end side.

United States Patent [191 Kondo Dec. 16, 1975 GRIPPER FOR USE WITH A LIFTING APPARATUS FOR GRIPPING AN ARTICLE DESIRED TO BE LIFTED [76] Inventor: Yoshizi Kondo, 2923-11, Togasaki,

Misato, Saitama, Japan [22] Filed: Jan. 14, 1975 [21] Appl. No.: 540,892

[52] US. Cl 294/102 R; 294/86 R; 294/114 [51] Int. C1. B66C 1/48 [58] Field of Search 294/101, 102 R, 102 A,

294/103, 114, 116, 86 R, 24/136 R, 136 A, 24/136 B, 136 L, 263 R, 263 SW, 263 B,

Primary ExaminerEvon C. Blunk Assistant Examiner-Johnny D. Cherry 57 ABSTRACT Disclosed is a gripper wherein between a pair of support plates extending from their upper ends connected to the lifting apparatus toward their lower ends there are provided a trapezoidal column presenting in cross section an isosceles trapezoid arranged with its bottom surface turned in said upper end and a pair of guide members having side surfaces arranged, respectively, in parallel with both inclination side surfaces of said trapezoidal column; and a pair of clamping members adapted to grip the article when allowed to slide toward said other end side are disposed, respectively, within a pair of elongate void spaces each defined between said inclination side surface of the trapezoidal column and said side surface of the guide member and united into one space on said lower end side.

10 Claims, 6 Drawing Figures US Patent Dec. 16,1975 Sheet 1 of2 3,926,468

FIG. 2

FIG.

US. Patent Dec. 16, 1975 Sheet 2 of2 3,926,468

FIG. 5

FIG. 4

GRIPPER FOR USE WITH A LIFTING APPARATUS FOR GRIPPING AN ARTICLE DESIRED TO BE LIFTED This invention relates to a gripper for use with a lifting apparatus for gripping an article desired to be lifted.

Conventionally, various types of grippers are used for a lifting apparatus such as a crane or winch. As an example, there is a gripper of scissors type which is employed to lift timber, stone or steel mass. This type of gripper indeed offers the convenience that when the gripper is lifted by a lifting apparatus, the article can automatically be gripped and lifted, but has the drawback that difficulties are presented in sufficiently firmly constructing a shaft section for permitting the scissors operation to be performed, a gripping section for gripping the article, or the like, so that such a gripper as is resistible to high load as applied can not be manufactured. As another example, there is a gripper which utilizes a wedging action occurring due to its longitudinal inclination surface. This type of gripper comprises a stationary section connected to a lifting apparatus and.

having a single longitudinal inclination hole vertically narrowed toward its lower end, and a pair of movable sections vertically inserted into said longitudinal inclination hole and vertically slidable along the inner wall surface of said longitudinal inclination hole, whereby to grip the article between said movable sections. In this case, when the gripper is lifted by a lifting apparatus, said movable section is allowed to slightly fall jointly with the article due to the gravity and simultaneously is pressed against the article surface due to said hole being inclined, to firmly grip the article. The heavier the lifted article, the stronger the gripping action result ing from the wedging action due to said inclination. Where that portion of said movable section for directly gripping the article is formed with a proper knurled or tooth-like irregularity, said gripping action is further increased in degree. In this case, however, loads resulting from the article weight are all applied from the inner wall surface of said inclination hole to said stationary section through said movable section. Accordingly, the aforesaid-section constituting members disposed in the load transmission path should have a mechanical strength high enough to resist said loads.

In recent years, as various kinds of machines, constructions or the like are enlarged in size, there has been an increasing demand for a gripper capable of safely, reliably and operationally easily lifting an article having a large weight. However, a gripper constructed as in said another example and yet having a mechanical strength sufficient to meet said demand is necessarily large-sized to become unsuitable for practical use. That is, from a practical point of view it is difficult to manufacture a gripper capable of lifting an article having a weight of more than tons. Under these circumstances, there has been expected the appearance of a small-sized and light gripper capable of safely, reliably and operationally easily lifting even an article which is large in weight.

The object of the invention is to provide a small-sized and light gripper capable of safely, reliably and operationally easily lifting a large weight article, and more particularly to provide a small-sized and light gripper which is so constructed as to prevent a large force, by dispersing loads due to the article weight, from being locally applied to the gripper, and therefore is resistible to high loads and yet able to be readily operated.

For attaining the above object, the gripper of the invention is provided with a pair of support plates arranged in parallel with each other and having at one end along their longitudinal or first direction a connection means connected to said lifting apparatus and extending toward the other end; a trapezoidal column extending in a second direction at right angles to the flat surface of said support plates and integrally connected at both ends, respectively, to said support plates and presenting in cross section an isosceles trapezoid arranged with its bottom surface turned up; a pair of guide members disposed with said trapezoidal column interposed therebetween and extending in said second direction and integrally connected at both ends, respectively, to said support plates, said guide members having side surfaces opposing, respectively, both inclination side surfaces of said trapezoidal column in parallel and spaced relation thereto and defining with said both inclination side surfaces a pair of elongate void spaces separated from each other at said one end side and united into one space at said other end side, said void spaces and said one space being respectively opened to the exterior; a pair of clamping members slidably inserted, respectively, into said pair of elongage void spaces and having at their tip end portions, respectively, a pair of grip surfaces which, when allowed to slide toward said other end, approach each other to grip an article desired to be lifted; and a pair of sliding means for moving said pair of clamping members through said void spaces, respectively.

When said gripper is connected by said connection means to a lifting apparatus such as a crane or winch, said first direction substantially coincides with the vertical direction. Said article desired to be lifted is first inserted from the other end sides of said support plates into an interspace between both clamping members spaced from each other by operation of said sliding means, and then said both clamping members are downwardly moved using said sliding means to grip said article therebetween. When, thereafter, the gripper is lifted using a lifting apparatus, said both clamping members are obliquely downwardly moved through said both void spaces, respectively, together with said article, thereby to more forcefully grip said article. The heavier the article, the stronger this gripping action. Where it is desired to release the article from the gripped condition thereof, the gripper is lowered by operating the lifting apparatus to permit the tip end of the article to abut on the ground or on other proper floor surfaces. When, thereafter, the gripper is further slightly lowered, the article is caused to relatively push up said clamping members. As a result, the article is released from said gripped condition.

The total amount of load applied to the gripper due to the article weight is applied to the two respective clamping members in a manner thus divided into two parts. Both clamping members respectively transmit said two-divided loads as applied thereto to the support plates through both inclination side surfaces of the trapezoidal column and both guide members. Namely, in the present gripper, provision of said trapezoidal column permits said total amount of load as applied to be transmitted to the support plates through the four transmission paths, whereas, in the conventional type of gripper having no such trapezoidal column, said total amount of load as applied is transmitted to the stationary section corresponding to the present support plate through the two transmission paths created from the two respective movable sections corresponding to the present clamping members to the respective corresponding inner Wall surfaces of said stationary section. Accordingly, in the gripper of the invention, local application of high load to the gripper is more reduced by said extent than in the conventional gripper having no trapezoidal column, and as a result the possibility of the gripper being locally damaged is also reduced by that extent. Such reduction effect can be said to have been attained owing to an appropriate disposition or arrangement of the members constituting the gripper. The foregoing fact indicates that the gripper of the invention is resistible to higher load as compared with the conventional type of gripper having the same weight, in other words, that the gripper of the invention can be more miniaturized with respect to the identical amount of load as applied.

For the purpose of improving the gripping ability of the present gripper, the clamping member can be formed at the grip surface with a proper irregularity such as a knurled or tooth-like irregularity, and further can be formed also at the grip surface with a. recess or depression conformed to the configuration of an article desired to be lifted, such as a semi-circular, elliptical, triangular or rectangular recess or depression. If, in this case, such recess or depression is further formed with said knurled or tooth-like irregularity, there will be able to be obtained a gripper which is suited for lifting a wide variety of articles. By providing reinforcing plates, respectively, for those outer wall portions of the respective support plates which are substantially opposite to those inner wall portions thereof for connection with both ends of the trapezoidal column, the present gripper can be so constructed as to be rendered suitable for lifting a larger weight article. It is to be noted that the present gripper constructed as described above can practically sufficiently resist a load of several hundreds of tons.

If, in the aforesaid sliding means, construction is so made that a pair of arms as constituting said sliding means are connected at one end to the clamping members and at the other end to a weight and are supported at a proper fulcrum, whereby the position of said fulcrum and the heaviness quantity of said weight are respectively so selected that the weight relation between opposite sides of the fulcrum is slightly so unbalanced that when the arms have been allowed to stand, the clamping members are raised without manual operation to permit the distance between both grip surfaces to be increased, the weight will be able to be readily manually lifted to enable the clamping members to grip the article, and further, when the gripped condition of the article has been released, the clamping members will be raised without manual operation to increase said distance between both grip surfaces, thereby to facilitate disengagement of the article from the gripper.

This invention can be more fully understood from the following detailed description when taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a perspective view of a gripper according to an embodiment of the invention with the interior thereof allowed to be seen through partially cutting away the constituent member thereof;

FIG. 2 is a view clearly illustrating the relation between the trapezoidal column and guide members of FIG. 1;

FIG. 3 is an enlarged view illustrating in detail the tooth sections formed in the clamping members of FIG.

FIG. 4 is a perspective view of a gripper according to another embodiment of the invention using support plates different from those of FIG. ll;

FIG. 5 is a view for explaining the gripper operation, illustrating the case wherein the gripper of FIG. 1 is in a state prior to the gripping operation; and

FIG. 6 is a view for explaining the gripper operation, illustrating the case wherein the gripper of FIG. 1 is in a state having gripped the article.

FIG. 1 shows an example of a gripper according to an embodiment of the invention. Reference numerals l0 and 12 denote parallel disposed support plates, which are formed, respectively, with elongate slits 14 and 16 at one end along their longitudinal or first direction. The support plates are rockably attached to a conn ection member 20 through a support rod 18 inserted through the elongate slits 14 and 16. The connection member 20 is attached to a lifting apparatus such as a crane or hoist utilizing a threaded section 22 extending further upwardly of said first direction. In this case, said first direction substantially coincides with the vertical direction of the illustration, and the support plates 10 and 12 are suspended with said one end side up and the other end side down. The other ends or lower ends of the support plates 10 and 12 are formed, respectively, with longitudinal grooves for permitting insertion therethrough of one end portion of an article 25 desired to be lifted such as a channel steel, steel sheet pile or the like.

At a substantially mid position between the upper and lower ends of the support plates 10 and 12 there is provided between said support plates a trapezoidal column 26 extending in a direction at right angles to the flat surface of the support plates .10 and 12, i.e., in a second direction, said trapezoidal column 26 being integrally connected at both ends, respectively, to said support plates, for example, by welding, and presenting in cross section an isosceles trapezoid arranged with its lower bottom surface turned up. Accordingly, both inclination side surfaces 28 and 30 of the trapezoidal column 26 (See FIG. 2) are respectively directed in a third direction at right angles to said first and second directions, i.e., in a horizontal direction parallel with said flat surface of said support plates, and are downwardly symmetrically inclined so as to be gradually made smaller in the distance between said both inclination side surfaces 28 and 30.

Plate-like guide members 36 and 38 are disposed with the trapezoidal column interposed therebetween said guide members 36 and 38 respectively having side surfaces 32 and 34 arranged in parallel with said inclination side surfaces 28 and 30. The guide members 36 and 38 extend in said second direction, and are each integrally connected at both ends, respectively, to the support plates 10 and 12, for example, by welding. As a result, a linearly extending void space 40 is defined, between the trapezoidal column 26 and the guide me mber 36, by the inclination side surface 28, side surface 32 and support plates 10, 12, as shown in FIG. 2. Further, between the inclination side surface 30 and the side surface 34 is formed another linearly extending void space 42 which is defined by the support plates 10 and 12 and inclined symmetrically with said void space 40. The upper portions of the void spaces 40 and 42 are opened to the exterior, respectively, at both sides of the trapezoidal column 26 while the lower portions thereof are united into one space and opened to the exterior.

Reference numerals 44 and 46 designate plate-like clamping members which are substantially the same in section as said void spaces 40 and 42 and snugly slidably inserted thereinto. The lower end portions of the clamping members 44 and 46 are formed with grip surfaces 48 and 49 (See FIG. 3) in parallel with a fiat plane including said first and second directions. When the clamping members 44 and 46 are allowed to slide downwardly, the grip surfaces 48 and 49 come to approach each other thereby to grip the article 25 inserted therebetween. In FIG. 1, said other end portion of the support plate 12 is cut away and indicated by one-dot chain lines, thereby to clearly illustrate various members provided between the support plates and 12. The upper end portions of the guide members 36 and 38 are formed, respectively, with projecting edges 50 and 52, which are used as fulcrums for sliding means 54 and 56 of which description is made below.

The sliding means 54 includes two pairs of projecting portions 58 provided on the top surface of the clamping member 44, a pair of arms 60 each pivotally rockably supported between each said pair of projecting portions 58, and a weight 62 attached between said pair of arms 60. Similarly, the sliding means 56 includes two pairs of projecting portions 64, a pair of arms 66 and a weight 68. The weights 62 and 68 have a weight sufficient to upwardly slide the clamping members 44 and 46 through the two respective pairs of arms 60, 66 rockable with the projecting edges 50 and 52 as the fulcrums, and yet the weight relationship between opposite sides of each said projecting edge is so selected that the difference between rocking forces acting in opposite directions with each said projecting edge as the fulcrum can be made small. As a result, it is easy to manually lift the weights 62 and 68 after insertion of the article 25 between the clamping members 44 and 46, thereby to downwardly slide said clamping members to grip the article 25. Further, when the article 25 has been released from the grip effected by said clamping members, the clamping members 44 and 46 can upwardly be slided with no manual operation, thereby to be completely disengaged from the article 25.

Further, for the purpose of permitting the grip surfaces 48 and 49 of the clamping members 44 and 46 to be inserted over the article 25 for reliably gripping the same 25, said grip surfaces are formed, respectively, with a plurality of tooth-like irreguralities 70 and 72 extending in said second directions. FIG. 3, in order to clearly illustrate the configuration of the tooth-like irregularalities 70 and 72, shows that cross section of the trapezoidal column 26, clamping members 44 and 46, and guide members 36 and 38 which is taken perpendicularly to said second direction. The line XY indicates said first direction, i.e., the vertical direction of the support plate 10. The configuration of the toothlike irregularities 70 illustrated in cross section, that is, a tooth configuration 74 is defined by a tooth tip A arranged substantially in parallel with the line XY, a first flat surface 71 indicated by a line AB extending at right angles to the line XY from said tooth tip A, and a second flat surface 73 indicated by a line AC defining an angle of substantially 0/2 with the line XY. In this case, 0 represents the vertical angle of the isosceles cross section of the trapezoidal column 26. The 0 and 6/2 are in association with the article gripping ability of the clamping members 44 and 46 and the readiness at the time of releasing the article from the gripped condition, and simultaneously are essential factors affecting the configuration, the size, accordingly the weight of the gripper as a whole. As a result, the 6 and 0/2 are selectively determined with the foregoing conditions synthetically taken into consideration. The 0 is chosen within the range of 20 to 40, or is preferably set at substantially 30. The grip surfaces 48 and 49 may be formed with the above-mentioned tooth-like irregularities and 72 in order to improve the gripping ability, or may alternatively be formed with another proper irregularity such as a knurled irregularity in accordance with the configuration, the surface condition or the weight of an article desired to be gripped. Further, for the purpose of gripping various configurations of articles, the grip surfaces 48 and 49 may be formed with concave portions being in conformity with the contour of such articles, said concave portions being formed with a knurled irregularity or tooth-like irregularity.

Referring to FIG. 4, reference numerals 76 and 78 denote reinforcing plates integrally attached to the support plates 10 and 12 from outside, for example, by welding. The reinforcing plates 76 and 78 are attached on those sides of the support plates 10 and 12 which are, respectively, substantially opposite to the positions for attachment of the trapezoidal column 26 to the support plates 10 and 12. The reinforcing plates 76 and 78 act to reinforce, against that load resulting from the weight of the article 25 which, when thearticle 25 has been gripped by the clamping members 44 and 46 and lifted by the lifting apparatus, is applied from said clamping members to said trapezoidal column 26 and said guide members 36, 38 and further to said support plates 10, 12, the above-mentioned members 44, 46, 36, 38, 10 and 12, thereby to enable the gripper to lift articles having a larger weight.

There will now be explained the operation in the case where the gripper is put to practical use. In FIGS. 5 and 6, there are respectively shown only the main sections necessary for explanation of the gripper operation.

FIG. 5 illustrates the condition wherein the clamping members 44, 46 are upwardly raised due to the action of the weights 62, 68 through the arms 60, 66 to permit the grip surfaces 48, 49 to be mutually spaced; and the article 25 is inserted between the grip surfaces 48 and 49 through a longitudinal groove 24 (See FIG. 4) up to the abutment against the tropezoidal column 26 but is not gripped. When, under this condition, the weights 62, 68 are manually lifted up, the clamping members 44, 46 are pushed down through the arms 60, 66, so that the grip surfaces 48, 49 approach each other to grip the article 25. When the weights 62, 68 are further lifted up to permit the grip surfaces to be sufficiently pressed, respectively, against the side surfaces of the article 25, the weights 62, 68 are prevented from dropping of themselves thus to permit the article 25 to be maintained in a pressed condition by the clamping members 44, 46. Next, when the gripper is lifted upwards by operating, for example, a crane (not shown), the article 25 is downwardly moved jointly with the clamping members 44, 46 to define a clearance 80 with the trapezoidal column 26 as shown in FIG. 6, and the clamping members 44, 46 are thereby permitted to more forcefully press the article 25. As a result, the tooth-like irregularities 70, 72 formed in said grip surfaces 48, 49 are permitted to firmly engage the side surfaces of the article thereby to render the article gripping more reliable. The heavier the article 25 to be lifted, the more forcefully the tooth-like irregularities engage the side surfaces of said article 25. As a result, the article gripping force is increased. When the condition of FIG. is shifted to the condition of FIG. 6, a small amount of displacement is relatively produced between the side surfaces of the article 25 and the tooth-like irregularities 70, 72. But damages producible in said side surfaces or irregularities due to such displacement remain extremely small.

Where it is desired to disengage the article 25 from the gripper, said crane is operated to lower the gripper thereby to permit the lower end of the article 25 to abut on the ground or on a proper floor surface. Then the substantially total amount of weight of the gripper so acts as to relatively raise the clamping members 44, 46 through said void spaces 40, 42. As a result, the clamping members 40, 42 are spaced from each other thus to release engagement of the tooth-like irregularities 70, 72 with the side surfaces of the article 25. At this time, the article 25 is upwardly moved through the clearance 80 relative to the clamping members 44, 46 to abut against the trapezoidal column 26, so that the clamping members 44, 46 are completely disengaged from the article 25 and upwardly automatically raised due to the action of the weights 62, 68 and the arms 60, 66 and thus brought to the condition of FIG. 5. Accordingly, the article 25 is rendered easily separable from the gripper. Where the gripping force is too great to release the gripped condition of the article 25 simply by utilizing the weight of the gripper, another weight is further applied to the gripper thereby to effect said release. To this end, as shown in FIG. 1, the support plates 10 and 12 are connected to, for example, a crane (not shown) through the support rod 18, the connection member and the threaded section 22. By operating the crane the gripper and the article gripped by means of this gripper are allowed to abut on the ground or on a proper floor surface and thereby brought into stoppage. When, thereafter, the connection member 20 is lowered by operating said crane further, the connection member 20 is permitted to fall along the elongate slits l4, 16 together with the support rod 18, so that the respective weights of the connection member 20 and other members connected thereto are additionally applied to raise the clamping members 44, 46 through the elongate slits l4, 16. Further, if a further additional load is applied to the lower ends of the elongate slits 14, 16 by abruptly dropping the connection member 20, the foregoing weight addition effect will be further increased, so that the article is easily released from engagement with the tooth-Like irregularities 70, 72.

In the case of a gripper for use in such operations as require no particular application of an additional weight, there is no necessity of providing the support plates 10, 12 with the above-mentioned elongate slits l4, 16. Accordingly, the support plates l0, 12 have only to be formed with a usual round through hole 19 for allowing passage therethrough of said support rod 18, as illustrated in FIG. 4.

Materials, of which the present gripper is formed, are all made of metal such as steel materials. But preferably, the clamping members 44, 46 are formed of die steel and the guide members 36, 38 of molybdenum steel.

What is claimed is:

1. A gripper for use with a lifting apparatus for gripping an article desired to be lifted comprising:

a pair of support plates arranged in parallel with each other and having at one end along their longitudinal or first direction a connection means connected to said lifting apparatus, and extending toward the other end;

a trapezoidal column extending in a second direction at right angles to the flat surface of said support plates and integrally connected at both ends, respectively, to said support plates and presenting in cross section an isosceles trapezoid arranged with its bottom surface turned up;

a pair of guide members disposed with said trapezoidal column interposed therebetween and extending in said second direction and integrally connected at both ends, respectively, to said support plates, said guide members having side surfaces opposing, respectively, both inclination side surfaces of said trapezoidal column in parallel and spaced relation thereto and defining with said both inclination side surfaces a pair of elongate void spaces separated from each other at said one end side and united into one space at said other end side, said void spaces and said one space being respectively opened to the exterior;

a pair of clamping members slidably inserted, respectively, into said pair of elongate void spaces and having at their tip end portions, respectively, a pair of grip surfaces which, when allowed to slide toward said other end, approach each other to grip said article; and

a pair of sliding means for moving said pair of clamping members through said void spaces, respec tively.

2. A gripper according to claim 1, further comprising a pair of reinforcing plates integrally attached, respectively, to said pair of support plates on those sides thereof which are respectively substantially opposite to the positions for connecting said trapezoidal column to said support plates.

3. A gripper according to claim 1 wherein the vertical angle of the isosceles cross section of said trapezoidal column is in the range of 20 to 40.

4. A gripper according to claim 1 wherein the vertical angle of the isosceles cross section of said trapezoidal column is chosen to be substantially 30.

5. A gripper according to claim I wherein said pair of grip surfaces each are formed with a plurality of teeth extending in said second direction, said teeth each being defined by a first plane formed extending at right angles to said grip surface from a tooth edge extending in said second direction along said grip surface and a second plane formed extending from said tooth edge toward the tip end of said clamping member at an angle of substantially 0/2 defined with said grip surface, said 6 representing said vertical angle of the isosceles cross section of said trapezoidal column.

6. A gripper according to claim 1 wherein said pair of sliding means each include a pair of projective edges formed on the top surface of said guide member, a pair of anns connected at one end, respectively, to said clamping member so as to rock said clamping member and rockable, respectively, with said pair of projective edges as fulcrums, and a weight attached between the other ends of said pair of arms.

7. A gripper according to claim 1 wherein said connection means includes a support rod inserted through a pair of round through holes formed respectively coaxially with said pair of support plates, and a connection one end between said pair of support plates through said support rod and having at the other end a threaded section for being attached to said lifting apparatus.

9. A gripper according to claim 1 wherein said pair of clamping members each are formed of die steel.

10. A gripper according to claim 1 wherein said pair of guide members each are formed of molybdenum steel. 

1. A gripper for use with a lifting apparatus for gripping an article desired to be lifted comprising: a pair of support plates arranged in parallel with each other and having at one end along their longitudinal or first direction a connection means connected to said lifting apparatus, and extending toward the other end; a trapezoidal column extending in a second direction at right angles to the flat surface of said support plates and integrally connected at both ends, respectively, to said support plates and presenting in cross section an isosceles trapezoid arranged with its bottom surface turned up; a pair of guide members disposed with said trapezoidal column interposed therebetween and extending in said second direction and integrally connected at both ends, respectively, to said support plates, said guide members having side surfaces opposing, respectively, both inclination side surfaces of said trapezoidal column in parallel and spaced relation thereto and defining with said both inclination side surfaces a pair of elongate void spaces separated from each other at said one end side and united into one space at said other end side, said void spaces and said one space being respectively opened to the exterior; a pair of clamping members slidably inserted, respectively, into said pair of elongate void spaces and having at their tip end portions, respectively, a pair of grip surfaces which, when allowed to slide toward said other end, approach each other to grip said article; and a pair of sliding means for moving said pair of clamping members through said vOid spaces, respectively.
 2. A gripper according to claim 1, further comprising a pair of reinforcing plates integrally attached, respectively, to said pair of support plates on those sides thereof which are respectively substantially opposite to the positions for connecting said trapezoidal column to said support plates.
 3. A gripper according to claim 1 wherein the vertical angle of the isosceles cross section of said trapezoidal column is in the range of 20* to 40*.
 4. A gripper according to claim 1 wherein the vertical angle of the isosceles cross section of said trapezoidal column is chosen to be substantially 30*.
 5. A gripper according to claim 1 wherein said pair of grip surfaces each are formed with a plurality of teeth extending in said second direction, said teeth each being defined by a first plane formed extending at right angles to said grip surface from a tooth edge extending in said second direction along said grip surface and a second plane formed extending from said tooth edge toward the tip end of said clamping member at an angle of substantially theta /2 defined with said grip surface, said theta representing said vertical angle of the isosceles cross section of said trapezoidal column.
 6. A gripper according to claim 1 wherein said pair of sliding means each include a pair of projective edges formed on the top surface of said guide member, a pair of arms connected at one end, respectively, to said clamping member so as to rock said clamping member and rockable, respectively, with said pair of projective edges as fulcrums, and a weight attached between the other ends of said pair of arms.
 7. A gripper according to claim 1 wherein said connection means includes a support rod inserted through a pair of round through holes formed respectively coaxially with said pair of support plates, and a connection member rockably connected at one end between said pair of support plates through said support rod and having at the other end a threaded section for being attached to said lifting apparatus.
 8. A gripper according to claim 1 wherein said connection means includes a support rod inserted through a pair of elongate slits formed, respectively, in said pair of support plates and extending from said one end side to said other end side in opposing relation to each other, and a connection member rockably connected at one end between said pair of support plates through said support rod and having at the other end a threaded section for being attached to said lifting apparatus.
 9. A gripper according to claim 1 wherein said pair of clamping members each are formed of die steel.
 10. A gripper according to claim 1 wherein said pair of guide members each are formed of molybdenum steel. 